According to a widely accepted constraint on the content of intentions, here called the exclusivity constraint, one cannot intend to perform another agent’s action, even if one might be able to intend that she performs it. For example, while one can intend that one’s guest leaves before midnight, one cannot intend to perform her act of leaving. However, Deborah Tollefsen’s (2005) account of joint activity requires participants to have intentions-in-action (in John Searle’s (1983) sense) that violate this constraint. I argue that the exclusivity constraint should not be accepted as an unconditional constraint on the contents of intentions-in-action: one may intend to perform a basic action that belongs both to oneself and to another agent. Based on the phenomenology of tool use, I first argue that intentions-in-action of one’s basic actions may be technologically extended, meaning that their contents are not restricted to concern the agent’s bodily movements. In analogy with this, I then argue that the phenomenology of some skillful joint activities supports the idea that one’s basic intentions-in-action may be socially extended, in violation of the widely accepted exclusivity constraint. Tollefsen’s account is specifically constructed to account for the joint activities of infants and toddlers who lack the capacity to think of others as planning agents and grasp their plan-like intentions (a capacity required by Michael Bratman’s (1992, 1993, 2009a, b) influential account of joint activity). At the end of the paper, I raise some doubts regarding the extent to which infants and toddlers have socially extended intentions-in-action.